Unevenness of a road surface can reduce the useful life of the road. When a vehicle rides over an uneven road surface, it tends to bounce vertically on its suspension resulting in dynamic loading of the road. The forces created in this way are significantly greater than the static load due to the weight of the vehicle. These increased forces create damaging stresses on the pavement materials used in road construction and consequently decrease road life.
Road unevenness is attributable to a number of sources including the curling or warping of adjacent concrete slabs used in road construction. Other sources of unevenness include wheel wear and sub-base movement. Diamond grinding can be used to eliminate road surface unevenness by using diamond-impregnated saw blades to grind away material creating a new, smoother road surface. Diamond impregnated blades can also be used to introduce grooves running parallel to the direction of vehicle travel. Such grooves act as drainage channels for water between tires and pavement, and thus reduce skidding and hydroplaning accidents without increasing the dynamic forces experienced by the road surface. An example of a pavement surfacing machine that utilizes diamond grinding is described in U.S. Pat. No. 4,588,231 to Silay et al., which is incorporated herein by reference in its entirety.
Diamond-impregnated saw blades are typically circular and are ganged together on a common axle to form a grinding head several feet wide. The head is rotated and held against the road surface as it is moved in a direction perpendicular to its axis to grind away a portion of the road surface. The spacing between the diamond blades determines the type of cut. Narrow spacing typically results in the pavement surface being ground, whereas increasing the spacing results in grooving. A mechanism is also normally employed to maintain the head at a uniform height, thereby causing the cut surface to be smooth and level under normal operating conditions. One such mechanism that is commonly employed is a set of wheels that ride along the cut surface of the pavement behind the cutting head and another set of wheels that ride along the uncut surface of the pavement a substantial distance ahead of the cutting head.
Diamond impregnated saw blades wear during grinding, however, and are expensive and time-consuming to replace. A key consideration in diamond grinding is the lifetime of the blades, which is maximized if the blades are rotated at a rate within a specified range of optimal angular velocities and if the torque load on the blades is held within a specified range. Excessive angular velocities or torque loads can result in the blades wearing more rapidly than necessary to perform a desired grind, while insufficient angular velocities or torque loading can polish the cutting surfaces of the blades. Polishing dulls the blades and severely inhibits their ability to perform road surface grinding.
The amount of material ground from a road surface is often referred to as the depth of cut. Achieving a smooth surface typically requires cutting from the pavement surface an amount of material that varies over time, thereby creating a varying depth of cut. However, when a surface is ground by a diamond-impregnated cutting head moving at a constant angular velocity and a constant forward speed, the torque loading of the head varies with the depth of cut required. In this environment, an operator must manually alter the forward travel speed of the diamond-impregnated cutting head in response to varying loads to maintain the angular velocity of the blade and the torque loading on the blade within their optimal ranges. This requires a high level of operator skill and creates a risk that the operator will select a forward travel speed that will damage the blades.